A study of Canadian diffuse and total solar radiation data—II Monthly average hourly horizontal radiation

Optimum collector slope for a liquid base active solar heating system employing flat-plate collectors was investigated. The optimum collector slope was studied as a function of (a) collector area, (b) yearly total heating load and (c) the ratio of space heating load to service hot water load. Collectors facing equator only were considered. Such a system was studied in four different Canadian locations having widely different climates. Under the above conditions, optimum collector slope varied with the amount of collector area employed. The optimum collector slope was invariant with the yearly total load itself, or the space heating to hot water load ratio. Contrary to the widely held belief, for the four locations investigated, the optimum collector slope varied from lat. − 10° to lat. + 15°; depending upon f_y, the fraction of load supplied by the solar system. When f_y is in 10–20 per cent range, optimum collector slope is lat. − 10° and increases almost linearly to lat.+ 15° at f_y in 80 per cent range. Consequently, when the fraction of load by the solar system is low, a flat roof may be profitably employed. On the other hand, when the fraction by the solar system is high, a south facing (for northern hemisphere) vertical wall may be profitably employed.     

An analytic model for the long-term performance of solar air heating systems

An analytic model is presented for the prediction of the monthly and yearly thermal performance of solar air heating systems. The effects of stratification in packed rock bed storage are explicitly taken into account. An expression for monthly solar fraction that depends on the important system and climatic variables is derived, which affords accurate predictions compared to corresponding f-chart calculations. The value of our analytic model, vis-a-vis calculational tools such as f-chart, is discussed. The method is applicable to all solar collector types as well as to load distributions of other than 24 hr/day.     

A thermo-economical optimization of a domestic solar heating plant with seasonal storage

In this study, the thermo-economic optimization analysis to determinate economically optimal dimensions of collector area and storage volume in domestic solar heating systems with seasonal storage is presented. For this purpose, a formulation based on the simplified P₁ and P₂ method is developed and solved by using MATLAB optimization Toolbox for five climatically different locations of Turkey. The results showed that the required optimum collector area in Adana (37 °N) for reaching maximum savings is 36 m²/house and 65 m²/house in Erzurum (39 °N) for same storage volume (1000 m³). The effects of collector efficiency on solar fraction and savings are investigated. The simulation results showed that the solar fraction and savings of the selective flat plate collector systems are higher than the other black paint flat plate collector systems.     

A feasibility study of solar heating in Iran

A single-glass, flat-plate solar collector for air heating is analyzed for an optimum tilt angle of 45° for Shiraz (29° 36′ N latitude, 52° 32′ E longitude, and elevation of 4500 ft). The absorbed and utilized solar energy, as well as the collector outlet air temperature, the glazing, and the blackened plate temperatures, are determined with respect to the incident solar energy, parametric with collector inlet air temperatures and flow rates and outside air temperature.A 10 ft² collector and an 8 ft³ rock storage are built to experimentally verify the analysis and obtain cost estimates. A 5000 ft² single-story building is considered for solar heating and economic evaluations. Based on an annual interest rate of 8 per cent amortization of the solar heating equipment over 15 yr, electrical energy costs of 3c/kWh, and fuel costs of $1·10 per 10⁶ B.t.u., the optimum collector area which results in minimum annual operating costs (of the solar heating system and the auxiliary heating unit) is determined. A net saving results because solar heating is employed. The feasibility study is extended to eleven other Iranian cities. It is found profitable to employ solar heating in cities with low annual rainfall and relatively cold winters. An effective evaporative cooling is obtained by spraying water over the rock storage during the summer.     

Performance analysis of hybrid solar-geothermal CO2 heat pump system for residential heating

A simulation study of hybrid solar-geothermal heat pump system for residential applications using carbon dioxide was carried out under different operating conditions. The system consists of a solar unit (concentric evacuated tube solar collector and heat storage tank) and a CO₂ heat pump unit (three double-pipe heat exchangers, electric expansion valve, and compressor). As a result, the differential of pressure ratio between the inlet and the outlet of the compressor increases by 19.9%, and the compressor work increases from 4.5 to 5.3 kW when the operating temperature of the heat pump rises from 40 °C to 48 °C. Besides, the pressure ratio of the compressor decreases from 3 to 2.5 when the ground temperature increases from 11 °C to 19 °C. The operating time of the heat pump is reduced by 5 h as the daily solar radiation increases. As the solar radiation increases from 1 to 20 MJ/m², the collector heat rises by 48% and the maximum collector heat becomes 47.8 kWh. The heating load increases by 70% as the indoor design temperature increases from 18 °C to 26 °C. However, the solar fraction is reduced from 11.4% to 5.8% because of the increases of the heating load.     

A simplified method for direct calculation of the annual load fraction of solar systems for space heating

Availability of data about long-term system performance is a first step towards economic analysis and optimization of solar systems. The use of detailed computer simulation techniques or even design methods such as the f-chart for evaluating system performance may be cumbersome for engineers and architects. In this paper, we present a simplified method to predict the annual system performance. The method allows direct calculation of the annual solar load fraction, for a specific location, as a function of collector area and design parameters. This method is based on a correlation of data generated by using the f-chart method. Because of its simplicity and excellent agreement with f-chart calculations, the present method should be a useful design aid for sizing and selecting solar systems for space heating.     

Optimization of tilt angle for solar panel: Case study for Madinah,Saudi Arabia

This article analyzes the optimal choice of the tilt angle for the solar panel in order to collect the maximum solar irradiation. In this paper, the collector surface is assumed to be facing toward equator. The study is based upon the measured values of daily global and diffuse solar radiation on a horizontal surface. It is shown that the optimal angle of tilt (β_opt) for each month, allows us to collected the maximum solar energy for Madinah site. Annual optimum tilt angle is found to be approximately equal to latitude of the location. It is found that the loss in the amount of collected energy when using the yearly average fixed angle is around 8% compared with the monthly optimum tilt β_opt.     

The influence of collector azimuth on solar heating of residential buildings and the effect of anisotropic sky-diffuse radiation

A liquid-base active residential solar heating system employing flat-plate collectors was examined. The two particular objectives of this study were: (a) to determine the influence of the collector azimuth on the fraction of the total demand supplied by the solar system, and (b) to consider the effect of sky-diffuse radiation being non-isotropic and the hourly radiation being asymmetric around solar noon vs the symmetric-isotropic model.The study showed that the influence of the collector azimuth varied with the collector slope. For low-sloped collectors, the collector azimuth had minimal effect on the energy supplied by the solar system. The azimuthal orientation had maximum effect when the collectors were vertically sloped. The maximum amount of energy supplied by the solar system was always obtained from collectors facing the equator.The final results were obtained by using either the symmetric-isotropic model or the asymmetric-anisotropic radiation model. These results differed from each other only by about 5 per cent maximum. The former model produced conservative results.The above calculations were carried out using meteorological data from three Canadian locations with different climates. Yearly heating loads of 10⁵, 10⁶ and 10⁷ MJ were employed at each location. Ratios of space-heating to service-hot-water loads were varied from 5 to 15.     

Optimum Tilt Angle for Solar Collectors

A solar collector is required to absorb solar radiation and transfer the absorbed energy into a heat transfer fluid with a minimum of heat loss. In assessing the performance of a collector, it is therefore important not only to determine its ability to absorb solar radiation but also to characterize its heat losses. The ability of a collector to absorb solar radiation is largely determined by its optical and geometric properties. One of the important parameters that affect the performance of a solar collector is its tilt angle with the horizontal. This is due to the fact that the variation in tilt angle affects the amount of solar radiation reaching the collector surface. In this study, a mathematical model is used to estimate the total (global) solar radiation on a tilted surface and to determine the optimum tilt angle for a solar collector in Izmir, Turkey. Total solar radiation on the solar collector surface with an optimum tilt angle is computed for specific periods. It is found that the optimum tilt angle changes between 0° (June) and 61° (December) throughout the year. In winter (December, January, and February) the tilt should be 55.7°, in spring (March, April, and May) 18.3°, in summer (June, July, and August) 4.3°, and in autumn (September, October, and November) 43°. The yearly average of this value was found to be 30.3° and this would be the optimum fixed tilt throughout the year.     

A design procedure for solar air heating systems

A natural extension of the design procedure for liquid-based solar space and water heating systems is a similar analysis for solar heating systems using air as the heat transfer fluid. In this paper, a solar air heating system incorporating a flat-plate air heater and packed bed thermal storage is described and a simulation model for the system is developed. The results of many simulations of the air heating system are used to establish the relationship between system performance and the system design and meteorological variables. The results are presented in analytic and graphical form, referred to as an f-chart for solar air heating systems. The results of simulations in several widely different climates suggest that the information presented in the f-chart is location independent. Methods of estimating the performance of air heating systems having a collector air capacitance rate and a storage capacity other than those used to generate the f-chart are included. A comparison of the performance of air and liquid based systems is afforded by a comparison of their respective f-charts. The air system is shown to perform better at high load fractions supplied by solar energy than a liquid-based system with the same collector thermal performance parameters.     

Experimental and theoretical investigation of a solar heating system with heat pump

In this study, the performance of a solar heating system with a heat pump was investigated both experimentally and theoretically. The experimental results were obtained from November to April during the heating season. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load met by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. The average seasonal heating performance values are 4.0 and 3.0 for series and parallel heat pump systems, respectively. A mathematical model was also developed for the analysis of the solar heating system. The model consists of dynamic and heat transfer relations concerning the fundamental components in the system such as solar collector, latent heat thermal energy storage tank, compressor, condenser, evaporator and meteorological data. Some model parameters of the system such as COP, theoretical collector numbers (N_c), collector efficiency, heating capacity, compressor power, and temperatures (T₁, T₂, T₃, T_T) in the storage tank were calculated by using the experimental results. It is concluded that the theoretical model agreed well with the experimental results.     

A parametric study of open loop solar heating systems—I

The performance of open loop solar heating systems is studied using a single non-dimensional equation. For any location the long term solar fraction depends primarily on three non-dimensional groups M, K and R. M is the ratio of energy available on the collector aperture to energy demand and is hence a collector sizing parameter. K is the ratio of a reference rate of collector heat loss to a reference rate of energy available and is a collector performance parameter. R is the number of days storage available. A correlation relating the solar fraction, E, to M, K and R is given and the range of validity of this correlation is examined. For open loop systems with short term storage, the correlation can be used as a design method for a large range of demand temperatures, demand patterns, collector types and orientations. Comparisons are made between the solar fraction calculated by an hour by hour computer model and that predicted by the design method. Agreement is good. Further comparisons are made between measured and predicted performance figures for a large 20 m² domestic hot water system. It is concluded that the correlation can be used as a reliable design method and will allow simple selection of optimum system designs.     

Experience with fully operational solar-driven 10-ton LiBr/H2O single-effect absorption cooling system in Thailand

A solar-driven 10-ton LiBr/H₂O single-effect absorption cooling system has been designed and installed at the School of Renewable Energy Technology (SERT), Phitsanulok, Thailand. Construction took place in 2005, after which this system became fully operational and has been supplying cooling for our main testing building's air-conditioning. Data on the system's operation were collected during 2006 and analyzed to find the extent to which solar energy replaced conventional energy sources. Here, we present these data and show that the 72 m² evacuated tube solar collector delivered a yearly average solar fraction of 81%, while the remaining 19% of thermal energy required by the chiller was supplied by a LPG-fired backup heating unit. We also show that the economics of this cooling system are dominated by the initial cost of the solar collector array and the absorption chiller, which are significantly higher than that of a similar-size conventional VCC system.     

Parabolic trough collectors for industrial process heat in Cyprus

The thermal utilization of solar energy is usually confined to domestic hot water systems and somewhat to space heating at temperatures up to 60 °C. Industrial process heat has a considerable potential for solar energy utilization. Cyprus has a small isolated energy system, almost totally dependent on imported fuels to meet its energy demand. The abundance of solar radiation together with a good technological base, created favorable conditions for the exploitation of solar energy in the island. The number of units in operation today corresponds to one heater for every 3.7 people in the island, which is a world record. Despite this impressive record no solar industrial process heat system is in operation today. The main problem for this is the big expenditure required for such a system and the uncertainty of the benefits. The objective of this work was to investigate the viability of using parabolic trough collectors for industrial heat generation in Cyprus. The system is analyzed both thermally and economically with TRNSYS and the TMY for Nicosia, Cyprus, in order to show the magnitude of the expected benefits. The load is hot water delivered at 85 °C at a flow rate of 2000 kg/h for the first three quarters of each hour from 8:00–16:00 h, 5 days a week. The system consists of an array of parabolic trough collectors, hot water storage tank, piping and controls. The optimum collector area for the present application is 300 m², the optimum collector flow rate is 54 kg/m² h and the optimum storage tank size is 25 m³. The system covers 50% of the annual load of the system and gives life cycle savings of about C£6200 (€10800). This amount represent the money saved from the use of the system against paying for fuel. The savings however refer to a non-subsidized fuel price, which will be in effect from 2003. The optimum system can deliver a total of 896 GJ per year and avoids 208 tons of CO₂ emissions to the atmosphere. The effect of various design changes on the system performance was investigated. The E–W tracking system (collector axis aligned in N–S direction) was found to be superior to the N–S one. The required load temperature affects the performance of the system as for higher temperatures the auxiliary energy required is bigger. Also a number of variations in the load use pattern have been investigated and presented in this paper. It was found that the bigger the load (double shift, full hour use pattern) the bigger the collector area required, the greater the first year fuel savings and the greater the life cycle savings of the installation. This means that it is more viable to apply solar industrial process heat to higher energy consumption industries.     

Optimization of a community solar heating system with a heat pump and seasonal storage

The optimization of a district solar heating system with an electric-driven heat pump and seasonal heat storage is discussed. The optimization process comprises thermal, economic and system control analyses. Thermal and economic optima have been derived for collector area and storage volume simultaneously. The effects of different collector types and building loads are also investigated. Summertime charging of the storage by off-peak electricity has been applied to avoid severe peaking of auxiliary in the winter and to reduce the yearly energy cost. The thermal co-storage of electric energy is emphasized with systems which fail to supply heat for the heat pump during the winter heating season.‡ It has been found that system cost-effectiveness is only slightly affected as storage volume is increased beyond the optimum size. Large variations in the optima for different system configurations were found. The minimum cost of heat supplied in an optimal 500-unit community with 90% solar fraction was estimated at 8.9 ¢ kWh⁻¹.     

The performance of a solar assisted heat pump water heating system

Analytical and experimental studies were performed on a solar assisted heat pump water heating system, where unglazed, flat plate solar collectors acted as an evaporator for the refrigerant R-134a. The system was designed and fabricated locally, and operated under meteorological conditions of Singapore. The results obtained from simulation are used for the optimum design of the system and enable determination of compressor work, solar fraction and auxiliary energy required for a particular application. To ensure proper matching between the collector/evaporator load and compressor capacity, a variable speed compressor was used. Due to high ambient temperature in Singapore, evaporator can be operated at a higher temperature, without exceeding the desired design pressure limit of the compressor, resulting in an improved thermal performance of the system. Results show that, when water temperature in the condenser tank increases with time, the condensing temperature, also, increases, and the corresponding COP and collector efficiency values decline. Average values of COP ranged from about 4 to 9 and solar collector efficiency was found to vary between 40% and 75% for water temperatures in the condenser tank varying between 30°C and 50°C. A simulation model has been developed to analyse the thermal performance of the system. A series of numerical experiments have been performed to identify important variables. These results are compared with experimental values and a good agreement between predicted and experimental results has been found. Results indicate that the performance of the system is influenced significantly by collector area, speed of the compressor, and solar irradiation. An economic analysis indicates a minimum payback period of about two years for the system.     

Experimental and theoretical study on a solar assisted CO2 heat pump for space heating

In this paper, a solar combi-system which consists of solar collector and a CO₂ heat pump is investigated experimentally and theoretically. Two experiments are primarily conducted to show the performance of this solar combi-system under different operation conditions. A system model is developed and validated in TRNSYS to analyze the influence of main components parameters. Subsequently, a multi-parameter optimization is carried out in GENOPT to obtain a final optimal result. The simulated results show that the optimized system can save 14.2% electricity and improve the solar fraction by 8%. The solar fraction of the optimized system can reach 71.1%. Finally, the optimized system performance is studied with the weather and load characteristics in Shanghai. Compared with the CO₂ HP heating system alone, the solar assisted system can save 1790.8 kWh electricity on the basis of year round operation.     

A theoretical study on area compensation for non-directly-south-facing solar collectors

Solar energy integrated with the building is an important approach for the synchronous development of solar energy and architecture. The energy gain of the solar collector integrated with the pitched roof has been greatly influenced by the roof azimuth and tilted angle. Investment cost of the collectors is mainly decided by the size of the collector area. Accordingly, it is significant for solar building design to economically determinate the area compensation of the solar collector at different azimuth and tilted angles. Take Kunming and Beijing as examples, area compensation for the flat-plate tube-fin solar collector used in southern regions and the evacuated tube collector with cylindrical absorbers used in northern regions in China have been theoretically calculated. The results to some extent show that the daily horizontal solar radiation, ambient temperature, the azimuth and tilted angle of the collector integrated into the roof have an influence on the area compensation. The azimuth angle and tilted angle of the roof are the main factors that influence the A/A₀, which is defined as the collector area ratio of the non-south-facing collectors to the south-facing ones with the optimal tilted angle. Comparative studies found that the range of A/A₀ for the evacuated tube collector used in the northern regions is close to that for the flat-plate tube-fin solar collector used in the southern regions. When the pitched roof tilted angle β ∈ [25°, 45°] and the azimuth angle ∣γ∣ ⩽ 30°, the collectors can intercept a lot of solar radiant-energy. Considering the economic situations of the ordinary consumers in China, the optimal area compensation A/A₀ ⩽ 1.30 is recommended in this paper.     

Theoretical study of multi-stage flash distillation using solar energy

Solar energy was utilized as a clean renewable heat source for operation of a multi-stage flash (MSF) distillation system in Benghazi to produce distilled water. The optimum T_h for operation of the MSF system with a typical flat-plate collector is 80°C; 1 m² of a flat-plate collector produces annually 8.2 m³ of distilled water at T_h = 80°C. When 1 m² of a compound parabolic collector (CPC) is used at T_h = 122°C, 13.1 m³ of distilled water are produced.     

Economic evaluation of a solar water heating system

This paper describes different methods of analysis of a solar water heating system to determine its economic viability. The solar fraction, required for this analysis, has been calculated with a stimulation program using hourly meteorological data of Singapore. A measured load profile, representing the average condition, was used for this program. The economic variables have been selected from the trends shown in previous years.When different economic optimization criteria were applied to the CIAS solar system, it was seen that both the life cycle saving and the annualized life cycle cost lead to the prediction of the same optimum collector area of 1200 m². The payback period and the internal rate of return analyses also predicted the same optimum collector area of 1000 m², which is smaller than that predicted by the method of life cycle costing. For the economic variables used in this analysis, the minimum payback period is about 14 years.